Heteroleptic N,N-donor pyrazole based Pt(II) and Pd(II) complexes: DNA binding, molecular docking and cytotoxicity studies

Analysis of the binding mechanism for a water-soluble Pd(II) complex containing β-amino alcohols with HSA applying experimental and computational methods

In the study ahead, the binding interactions of the [Pd (HEAC) Cl2] complex with human serum albumin (HSA) protein have been assayed in vitro (pH= 7.40) utilizing computational and experimental procedures. The mentioned complex was synthesized as a water-soluble complex from {2-((2-((2-hydroxyethyl)amino)ethyl)amino) cyclohexanol} ligand = HEAC. The results of electronic absorption and circular dichroism investigations illustrated that the hydrophobicity of the Tryptophan microenvironment in HSA undergoes the changes by binding to the Pd(II) complex without substantial perturbations on the protein secondary structure. The fluorescence emission spectroscopy analysis revealed that with rising temperature, the quenching constant (Ksv) in the Stern-Volmer's relation decreases; so, it can be said that the interaction process is along with a static quenching mechanism. The values of 2.88 × 105 M-1, and 1.26 represent the binding constant (Kb) and the number of the binding sites (n), respectively. The Job graph showed the maximum point at χ = 0.5, which means organizing a new set with 1:1 stoichiometry. Thermodynamic profile (ΔH < 0, ΔS < 0, and ΔG < 0) has affirmed that van der Waals forces and hydrogen bonds have a basic function in the Pd(II) complex-albumin bindings. The ligand-competitive displacement studies utilizing warfarin and ibuprofen have represented that Pd(II) complex interacts with albumin by site II (subdomain IIIA). The computational molecular docking theory approved the results of the site-competitive tests; also, it indicated the existence of hydrogen bonds and van der Waals forces in Pd(II) complex-albumin interactions.Communicated by Ramaswamy H. Sarma.

Interaction studies of water-soluble Zn(II) complex with calf thymus DNA using biophysical and molecular docking methods"

The binding between a fluorescent water-soluble Zn(II) complex of {2-[N-(2-hydroxyethylammonioethyl) imino methyl] phenol} and calf thymus DNA (ct-DNA) was investigated using spectroscopic techniques. The complex was prepared and identified by FT-IR, and 1H NMR spectroscopies. The significant changes in the absorption and the circular dichroism spectra of ct-DNA in the presence of the Zn(II) complex implied the interaction between the Zn(II) complex and ct-DNA. Upon addition of ct-DNA, the fluorescence emission intensity of the Zn(II) complex was increased and indicated the interaction between the Zn(II) complex and ct-DNA was occurred. The binding constant values (Kb) resulted from fluorescence spectra clearly showed the Zn(II) complex affinity to ct-DNA. The fluorescence studies also approved the static enhancement mechanism in the Zn(II) complex-DNA complexation process. The thermodynamic profile exhibited the exothermic and spontaneous formation of ct-DNA-Zn(II) complex system via hydrogen bonds and van der Waals forces. The competitive fluorescence investigation by methylene blue (MB), and Hoechst 33258 demonstrated that the Zn(II) complex could replace the DNA-bound Hoechst and bind to the minor groove binding site in ct-DNA. The viscosity changes were negligible, representing the Zn(II) complex binding to DNA via the groove binding mode. Molecular docking simulation affirmed that the Zn(II) complex is located in the minor groove of ct-DNA near the DG12, DA17, DA18, and DG16 nucleobases.

A biophysical study of the interactions of palladium(II), platinum(II) and gold(III) complexes of aminopyridyl-2,2'-bipyridine ligands with RNAs and other nucleic acid structures

Metal compounds form an attractive class of ligands for a variety of nucleic acids. Five metal complexes bearing aminopyridyl-2,2'-bipyridine tetradentate ligands and possessing a quasi-planar geometry were challenged toward different types of nucleic acid molecules including RNA polynucleotides in the duplex or triplex form, an RNA Holliday four-way junction, natural double helix DNA and a DNA G-quadruplex. The binding process was monitored comparatively using different spectroscopic and melting methods. The binding preferences that emerge from our analysis are discussed in relation to the structural features of the metal complexes.

Synthetic approach toward spiro quinoxaline-β-lactam based heterocyclic compounds: Spectral characterization, SAR, pharmacokinetic and biomolecular interaction studies

Series of spiro quinoxaline-β-lactam based heterocyclic compounds (QL 1 - QL 21) were synthesized and characterized by spectroscopic techniques like ¹H-NMR, LC-MS, FT-IR spectroscopy and elemental analysis. The binding mode and binding strength between compounds and calf thymus-DNA were estimated by UV-visible spectroscopy, viscosity measurement and molecular docking studies. The compounds bind with the DNA through partial intercalation mode. In the absorption titration experiment, the K_b values for all the synthesized compounds were found in the range of 0.24-0.64 × 10⁵ M^-1. The protein binding studies of all the synthesized compounds were evaluated by absorption titration experiment, and the K_b value for all the compounds was obtained in the range of 0.030-1.571 × 10⁴ M^-1. The compounds were screened against two Gram (+ve) and three Gram (-ve) bacteria for antimicrobial activity. The MIC values for all the synthesized compounds were found in 95-255 µM. The LC₅₀ values (cytotoxicity) of the synthesized compounds (QL 1-QL 21) were found in the range of 4.00-12.89 µg/mL. The ADME study was carried out using the online platform SwissADME and admetSAR to evaluate the pharmacokinetic profile of all the synthesized compounds. All the compounds were screened for anticancer activity against the human osteosarcoma (MG-63) cell line. The result shows that all the compounds exhibit effective anticancer activity.Communicated by Ramaswamy H. Sarma.

Experimental and Molecular Docking Studies on the Interaction of a Water-Soluble Pd(II) Complex Containing β-Amino Alcohol with Calf Thymus DNA

The interaction of water-soluble and fluorescent [Pd (HEAC) Cl₂] complex, in which HEAC is 2-((2-((2-hydroxyethyl)amino)ethyl)amino) cyclohexanol, with calf thymus DNA (ct-DNA) has been studied. This study was performed using electronic absorption and fluorescence emission spectroscopies, cyclic voltammetry and circular dichroism analyses, dynamic viscosity measurements, and molecular docking theory. From hypochromic effect observed in ct-DNA absorption spectra, it was found that the Pd(II) complex could form a conjugate with ct-DNA strands through the groove binding mode. The K_b values obtained from fluorescence measurements clearly assert the Pd(II) complex affinity to ct-DNA. The fluorescence quenching of the DNA-Hoechst compound following the successive additions of the Pd(II) complex to the solution revealed that the Pd(II) complex is located in the ct-DNA grooves, and Hoechst molecules have been released into solution; moreover, the resulting measurements from relative viscosity authenticate the Pd(II) complex binding to the grooves. Negative quantities of thermodynamic parameters imply that the Pd(II) complex binds to ct-DNA mainly by the hydrogen bonds and van der Waals forces; also, the Gibbs-free energy changes show the exothermic and spontaneous formation of the Pd(II) complex-DNA system. The electrochemical behavior of the Pd(II) complex in the attendance of ct-DNA was investigated using the cyclic voltammetry method (CV). Several quasi-reversible redox waves were observed along with increasing the anodic/cathodic peak currents, as well as a shift in anodic/cathodic peak potentials. Circular dichroism (CD) observations suggested that the Pd(II)-DNA interaction could alter ct-DNA conformation. The results of molecular modeling confirmed that groove mechanism is followed by the Pd(II) complex to interact with ct-DNA.

DNA interaction, anticancer, cytotoxicity and genotoxicity studies with potential pyrazine-bipyrazole dinuclear µ-oxo bridged Au(III) complexes

Pyrazine-bipyrazole-based µ-oxo bridged dinuclear Au(III) complexes were synthesized and characterized by various spectrometric (¹H-NMR, ¹³C (APT) NMR, FT-IR, Mass spectrometry) and analytical techniques (elemental analysis and conductance measurement). The evaluation of DNA binding activity by UV-Vis absorption spectra and viscosity measurement demonstrated that all the compounds intercalate in between the stacks of DNA base pair and the binding constant values were observed in the range of 5.4 × 10⁴-2.17 × 10⁵ M^-1. The molecular docking study also supports the intercalation mode of binding. The anti-proliferation activity of complexes on A549 (Lung adenocarcinoma) cells by MTT assay demonstrated IC₅₀ values in the range of 47.46 -298.12 μg/mL. The genotoxicity of compounds was checked by smearing observed in the DNA of S. pombe cell under the influence of complexes. The in vivo cytotoxicity of compounds against brine shrimp demonstrated the LC₅₀ values in the range of 4.59-27.22 μg/mL. The promising results of the Au(III) complexes received significant attention and make them suitable for the new metallodrugs after the detailed mechanistic biological study.

Elucidation of DNA binding interaction of new Cu(II)/Zn(II) complexes derived from Schiff base and L-tryptophan amino acid: a multispectroscopic and molecular docking approach

Herein, we describe the synthesis, structural elucidation, and DNA interaction of newly synthesized Cu(II) and Zn(II) complexes, i.e., [Cu(SB)(L-trp)(H₂O)₂]NO₃ (1) and [Zn(SB)(L-trp)(H₂O)₂]NO₃ (2) (SB = Schiff base obtained from the reaction between o-vanillin and 2-amino-2-methylpropane-1,3-diol; L-trp = L-tryptophan). From the analysis, a six-coordinated environment around the Cu(II) or Zn(II) center is proposed. The ability of the complexes to bind with calf thymus DNA was examined by optical spectroscopy (UV-vis titrations and steady-state fluorescence emission) and viscosity measurements. The vivid experimental results revealed that complexes 1 and 2 avidly bind to DNA through surface and groove binding modes, albeit with dissimilar intrinsic binding constants (1.54 × 10⁴ and 1.36 × 10⁴ M^-1 for 1 and 2, respectively). Both complexes can displace ethidium bromide (EB) to some extent from the intercalated EB-DNA system, resulting in fluorescence quenching. Additional experiments such as [Fe(CN)₆]^4--induced quenching and thermal melting confirmed the electrostatic and groove binding mode. Furthermore, molecular docking studies verified that both complexes locate in the DNA minor groove by surface binding and were stabilized through weak intermolecular forces. The binding affinity of the lowest energy docked pose was found to be -5.37 kcal/mol for complex 1 and - 5.18 kcal/mol for complex 2. The present work is expected to pave the way for the synthesis of DNA-targeting Cu(II)/Zn(II) metal complexes for the development of chemotherapeutic agents.

Cell apoptosis induced by ciprofloxacin based Cu(II) complexes: cytotoxicity, SOD mimic and antibacterial studies

The current cancer research focuses on the design and synthesis of chemical compounds that can modulate cell apoptosis or programmed cell death. So we synthesized and characterized ciprofloxacin based copper(II) complexes and studied their anticancer activity against HCT 116 cancer cells by MTT assay. We further investigated the influence of compound-2 (better IC₅₀ value than cisplatin) on cancer cells to know the exact mechanism of anticancer activity. The distinct morphological change of cells due to compound-2 was observed in bright field microscopy. The trypan blue assay clearly demonstrated inhibition of cell viability. The clonogenic ability inhibition assay showed a low percentage of the plating efficiency of HCT 116 cells. The mechanism of cell death, either apoptotic or necrotic was distinguished by annexin V-FITC/PI (propidium iodide) staining assay and LDH (lactate dehydrogenase) release assay. The positive annexinV/PI cells in presence of compound-2 and absence of LDH in the LDH release assay confirmed the cell apoptotic mechanism of cell death. We also checked in vitro antibacterial activity of compounds against Gram^(-ve) and Gram^(+ve) bacteria in terms of MIC (minimum inhibitory concentration) and the data were in good agreement with the standard drug data. SOD mimic activity of synthesized Cu(II) complexes was also studied in terms of IC₅₀ value. The brine shrimp lethality bioassay was also performed to evaluate the cytotoxic properties of the Cu(II) complexes.Communicated by Ramaswamy H. Sarma.